Heater and method of manufacturing same

ABSTRACT

Provided is a heater in which heater patterns are provided in parallel between terminals. Each terminal is divided into a divided terminal having electrical conduction only with one heater pattern, and a divided terminal having electrical conduction only with the other heater pattern. After a heater body is fabricated, in a state prior to mounting a feed bolt, resistance adjustment is performed with respect to each of a virtual series path formed between the divided terminals and a virtual series path formed between the divided terminals. Then the feed bolt is mounted to each terminal, whereby a plurality of virtual series heater patterns are placed in electrical conduction with each other, thus forming a parallel circuit.

FIELD OF INVENTION

The present invention relates to a heater that is suitably used as aheater for heating a wafer in a semiconductor manufacturing process, andits production.

BACKGROUND ART

Heaters such as ceramic heaters have been widely used as heaters forheating wafer in manufacturing process of semiconductor and liquidcrystal. One heater design has been known (in Patent Document 1, forexample), in which a heater element made from conductive material suchas PG (pyrolytic graphite) is formed on a base between terminals in apredetermined heater pattern of helical, spiral or meandering shape, forexample.

Such heater includes a serial-type heater 10 (FIG. 7) in which a heaterpattern 11 is formed between terminals A and B in series and aparallel-type heater 20 (FIG. 8) in which heater patterns 21 and 22 areformed respectively between terminals A and B in parallel, either one ofwhich may be selected to perform an optimal heating performancedepending upon shape or outer diameter of a work to be heated, purposeof use of a device to which the heater is incorporated, power source tobe applied, for example. The heater pattern 11 in the serial-type heater10 of FIG. 7 and the heater patterns 21, 22 in the parallel-type heater20 of FIG. 8 are shown as simplified patterns by way of examples,respectively.

When a work such as a semiconductor wafer is heated by a heater, therewould be a tendency in most applications that the outer peripheral areahas a temperature lower than the inner peripheral area. Accordingly, aheater is usually designed such that the outer peripheral area is givena smaller electric resistance and the inner peripheral area is given agreater electric resistance in order that the outer and inner peripheralareas should be heated substantially uniformly. Alternatively, it may berequired in some cases to heat different areas such as outer and innerperipheral areas, upper and lower areas, right-side and left-side areasto different temperatures. To satisfy the requirements in the respectivedesigns, it is necessary to give a specific electric resistance propertyto the heater pattern.

For example, the heater pattern 11 of the serial-type heater 10 shown inFIG. 7 comprises, in a radial direction, an outer peripheral section 11a, an intermediate section 11 b and an inner peripheral section 11 c ineach semicircle. An example of adjustment for giving optimal resistancesto the respective sections for uniform heating will be described inreference to FIG. 9. Measurement points P1 to P4 are plotted formeasuring resistance values at the respective sections. In this case, asection from the terminal A to the measurement point P1 (the outerperipheral section 11 a) should have a resistance value r1=1.59 ohms, asection from the measurement point P1 to the measurement point P2 (theintermediate section 11 b) should have a resistance value r2=0.96 ohms,a section from the measurement point P2 to the measurement point P3(inner peripheral section 11 c) should have a resistance value r3=1.36ohms, a section from the measurement point P3 to the measurement pointP4 (the intermediate section 11 b) should have a resistance valuer4=0.96 ohms and a section from the measurement point P4 to the terminalB should have a resistance value r5=1.59 ohms (each sectional resistancevalue r1 to r5 is a reference value after being adjusted).

With regard to the heater pattern 11 of the serial-type heater 10, it ispossible to measure and adjust the resistance values sequentially fromthe terminal A, the measurement points P1 to P4 and to the terminal B.More specifically, the resistance value from the terminal A to eachmeasurement points (including the terminal B) is exactly the same withthe total sum of the sectional resistance values for the sectionstherebetween (for example, the resistance value from the terminal A toP4 should be identical to r1+r2+r3=3.91 ohms). Accordingly, theresistance adjustment is performed relatively easily in such mannerthat, after measuring the resistance values between the terminal A andthe measurement points P1 to P4 and the measurement points B in theorder, each measured resistance value should be adjusted to become equalto the total sum of the preceding sectional resistance values. Inpractice, the element of the heater pattern 11 is formed at first alittle bit thicker to provide a resistance value of a little bit smallerthan the design resistance value, which should then be partly scrapeddepending upon the resistance values measured at the respectivemeasurement points for the resistance adjustment.

However, with the parallel-type heater 20 (FIG. 8) in which the heaterpatterns 21, 22 are formed in each semicircles between the terminals Aand B, the resistance values measured at the respective measurementpoints in the heater patterns 21, 22 have two different current routs,one starting from the terminal A to the measurement point (A-Pn) and theother starting from the measurement point to the terminal A (Pn-A).Accordingly, when a man tries to adjust the resistance value by scrapingthe element in a measured section, this will influence and change theresistance values in other sections. The resistance adjustment should becarried out taking such influence into consideration, which shouldrequire a great deal of skill.

This will be described in more detail in reference to FIG. 10. Thedesign resistance value of the heater 20 is determined to be 1.6 ohms,and measurement points P11 to P14 are allotted in the heater patterns21, 22 between the terminals A and B. In this case, a section betweenthe terminal A and the measurement point P1 (the outer peripheralsection 21 a and the intermediate section 21 b of the heater pattern 21)should have a resistance value r11=1.01 ohms, a section between themeasurement points P11 and P12 (the inner peripheral section 21 c andthe intermediate section 21 b of the heater pattern 21) should have aresistance value r12=0.97 ohms, a section between the measurement pointP12 and the terminal B (the outer peripheral section 21 a of the heaterpattern 21) should have a resistance value 03=0.68 ohms, a sectionbetween the terminal B and the measurement point P13 (the outerperipheral section 22 a and the intermediate section 22 b of the heaterpattern 22) should have a resistance value r14=1.01 ohms, a sectionbetween the measurement points P13 and P14 (the inner peripheral section22c and the intermediate section 22 b of the heater pattern 22) shouldhave a resistance value r15=0.97 ohms, and a section between themeasurement point P14 and the terminal A (the outer peripheral section22 a of the heater pattern 22) should have a resistance value r15=0.68ohms (each sectional resistance value r11 to r15 is a reference valueafter being adjusted).

Each sectional resistance value by design is shown in Table 1. It is sodesigned that the route A-B and the route B-A are in parallel and havethe same resistance value (1.61 ohms), and the measurement sections insymmetric position in the respective routes (sections A-P11 and B-P14,sections P11-P12 and P13-P14, sections P12-B and P12-A) have the sameresistance values. In the parallel patterns, there are two parallelrouts at the respective measurement points, one starting from theterminal A and the other ending at the terminal A. Accordingly, by wayof example, the resistance value at the section (A-P11) between theterminal A and the measurement point P11 is calculated by the equation1/[1/r11+1/(r12+r13+r14+r15+r16)]=1/(1/1.26+1/5.18)=1.01 ohms (see FIG.10(b).

TABLE 1 Measurement Resistance Value Section by Design A-P11 1.26 (r11)P11-P12 1.19 (r12) P12-B 0.77 (r13) B-P13 1.26 (r14) P13-P14 1.19 (r15)P14-A 0.77 (r16)

As described above, the parallel pattern has two routes at therespective measurement points, one from the terminal A thereto and theother to the terminal A therefrom. Accordingly, contrary to the serialpattern, the resistance values at the respective measurement points donot consistent with the total sum. When a section is subjected to theresistance adjustment, the resistance value of other sections shouldalso be changed, so that precise adjustment is extremely difficult. Theadjustment is especially difficult when the section A-Pn and the sectionPn-(B)-A forming the parallel routes have greatly different resistancevalues, which requires a skillful technique in machining the element.

This will be described in more detail by giving a concrete example. Itis practically difficult that the same thickness is given to the elementforming the heater patterns 21, 22 of the parallel-type heater 20 overthe entire length, even with the controlled CVD conditions in the heaterproduction. In most cases, the element has different thickness portionby portion. Due to this reason, the resistance values r11 to r16measured at the respective measurement points P11, P12, B, P13 and P14could become greatly different from the reference values shown in FIG.10(b), which may actually be as shown in FIG. 11, for example. Thisexample shows that, the element of the heater patterns 21, 22 of theparallel-type heater 20 was formed to have almost the prescribedthickness in its upper area, so that the sectional resistance valuesr11, r12 and r13 in the upper areas are all almost equal to thereference values shown in FIG. 10(b), which would not require cutting ormachining of the element for the resistance adjustment. However, theelement was formed in its lower area somewhat thicker than theprescribed one, so that the sectional resistance values r14 to r16 inthe lower areas are all lower than the reference values shown in FIG.10(b) by the order of 0.8 to 1.1 ohms, which makes it necessary toscrape and make thinner the element in these areas, so as to adjustthese sectional resistance values to become substantially equal to therespective reference values.

For example, the measured resistance value in the measurement sectionB-P13 is 0.90 ohms, which is lower than the resistance value r14=1.01ohms shown in FIG. 10(b) for the same section, which requires theresistance adjustment by scraping the heater element. However, as knownfrom the aforesaid equation, the resistance value in one section shouldbe related with the resistance values in other sections, which meansthat if the sectional resistance value r14 should be changed, theresistance values in the preceding sections (any section originallyhaving a resistance value nearly equal to the reference value requiringno resistance adjustment and/or any already resistance-adjustedsections). Accordingly, when the resistance adjustment is to be carriedout for a particular section, it is necessary to scrape the element,while predicting its influence to change the resistance values in othersections together with an amount of such changes, and in considerationof an overall balance. This will require a skillful technique with manyexperiences.

PRIOR ARTS Patent Documents

Patent Document 1: Japan Patent Publication No. 1999(Hei11)-354260(A)

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Accordingly, the problem to be solved by the present invention is tomake it possible to easily perform pre-production resistance adjustment,with no need of a skill, for a parallel-type heater having parallelheater patterns between terminals, while not detracting from intendedfunction of the heater.

Means for Solving the Problems

According to claim 1 of the present invention, there is provided aparallel-type heater wherein a plurality of heater patterns are formedin parallel between a pair of terminals to which power supply bolts arefitted respectively, characterized in that each terminals is dividedinto a plurality of spaced segmental terminals of the same number assaid heater patterns, said plural segmental terminals being electricallyconnected with each other by said power supply bolt, wherein a pluralityof imaginary serial heater patterns are formed between one of saidsegmental terminals divided from one of said terminals and one of saidsegmental terminals divided from the other terminal when said powersupply bolt are not yet fitted, whereas said plural imaginary serialheater patters are electrically connected with each other to formparallel circuits when said power supply bolts are fitted.

According to claim 2 of the present invention, in the parallel-typeheater of claim 1, it is characterized in that a head of said powersupply bolt is in contact with a heater element forming said heaterpattern directly or via a washer made by conductive material.

According to claim 3 of the present invention, in the parallel-typeheater of claim 1 or 2, it is characterized in that first and secondheater patterns are formed in parallel between a pair of said terminals,each terminal being divided into a first segmental terminal to beelectrically connected only with said first heater pattern and a secondsegmental terminal to be electrically connected only with said secondheater pattern.

According to claim 4 of the present invention, in the parallel-typeheater of claim 3, it is characterized in that each of said first andsecond segmental terminals is formed in substantially a semicircularring shape, said first and second heater patterns being insulated witheach other by a gap extending in a radial direction between saidsegmental terminals.

According to claim 5 of the present invention, in the parallel-typeheater of claim 1 or 2, it is characterized in that first to fourthheater patterns are formed in parallel between a pair of said terminals,each terminal being divided into a first segmental terminal to beelectrically connected only with said first heater pattern, a secondsegmental terminal to be electrically connected with said second heaterpattern, a third segmental terminal to be electrically connected withsaid third heater pattern and a fourth segmental terminal to beelectrically connected only with said fourth heater pattern.

According to claim 6 of the present invention, in the parallel-typeheater of claim 5, it is characterized in that each of said first tofourth segmental terminals is formed in substantially a quadrant ringshape, said first to fourth heater patterns being insulated with eachother by gaps extending in radial and circumferential directions betweensaid segmental terminals.

According to claim 7 of the present invention, there is provided aproduction of the parallel-type heater of one of claims 1 to 6,characterized by steps of producing a heater body having a plurality ofheater patterns in parallel between a pair of terminals, performingresistance adjustment for each of said imaginary serial heater patternsformed between one segmental terminal of one terminal and one segmentalterminal of the other terminal before fitting said power supply bolts tosaid terminals, and then fitting said power supply bolts to saidterminals so that said plural imaginary serial heater patterns becomeelectrically connected with each other to form a parallel circuit.

Advantages of Invention

In accordance with the present invention, in a state where the powersupply bolts are not yet fitted to the terminals, a plurality ofimaginary serial heater patterns are formed between one of the segmentalterminals divided from one terminal and one of the segmental terminalsdivided from the other terminal. Accordingly, it is possible torelatively easily perform the resistance adjustment for the imaginaryserial heater patterns, in the same way as for the conventionalserial-type heaters. Thereafter, the power supply bolts are fitted tothe terminals so that the plural imaginary serial heater patterns becomein contact with each other to form a parallel circuit, which means thatthe final product will be the same as the conventional parallel-typeheaters. Thus, it is possible to stably and efficiently provide aproduct having a small individual difference.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overall plan view of a parallel-type heater (in a completestate where the power supply bolts are fitted) according to anembodiment (Embodiment 1) of the present invention.

FIG. 2(a) is an enlarged plan view showing a part around the terminal ofFIG. 1 and (b) is a cross-section taken along the section line I-I in(a).

FIG. 3 is an overall plan view of the heater in a state where the powersupply bolts are removed.

FIG. 4(a) is an enlarged plan view showing a part around the terminal ofFIG. 3 and (b) is a cross-section taken along the section line II-II in(a).

FIG. 5 is an explanatory view showing the manner of resistanceadjustment for the heater of FIG. 3 and FIG. 4.

FIG. 6 is an overall plan view of a parallel-type heater according toanother embodiment (Embodiment 2) of the present invention, which isshown in a state where the power supply bolts are removed as in FIG. 3

FIG. 7 is an overall plan view of a serial-type heater according to theprior art.

FIG. 8 is an overall plan view of a parallel-type heater according tothe prior art.

FIG. 9(a) is an overall plan view showing the serial-type heater of FIG.7 in which resistance measurement points are plotted and (b) is anexplanatory view showing the manner of resistance adjustment for thisheater.

FIG. 10(a) is an overall plan view showing the parallel-type heater ofFIG. 8 in which resistance measurement points are plotted and (b) is anexplanatory view showing the manner of resistance adjustment for thisheater.

FIG. 11 is an explanatory view showing, by way of example, that it isdifficult to conduct resistance adjustment for the parallel-type heaterof FIG. 8.

EMBODIMENTS OF INVENTION

The present invention will be described in detail in reference to someembodiments thereof.

Embodiment 1

FIG. 1 and FIG. 2 show a parallel-type heater 30 according to oneembodiment (Embodiment 1) of the present invention. In this heater 30,symmetrically designed heater patterns 31, 32 are formed betweenterminals A, B.

This heater 30 comprises a heater body 36 of a triple-layered structurecomprising a disc-shaped heater base 33, at least its front and backsurfaces being made from insulating material such as PBN (pyrolyticboron nitride, including one into which a small amount of carbon isincorporated), heater element 34 made from conductive material such asPG (pyrolytic graphite) forming the heater patterns 31, 32 (their centerlines being shown by dashed lines), and an overcoat 35 made frominsulating material such as PBN. The heater body 36 may be manufacturedby a routine procedure comprising the steps of vapor-depositing heaterelement 34 onto the heater base 33, partly removing the heater elementto form the heater patterns 31, 32, forming the overcoat 35 thereon, andthen removing opposite end portions of the overcoat 35 to expose theheater element 34 to thereby form the terminals A, B. The overcoat 35 isshown in FIG. 2(b) but omitted in FIG. 1 and FIG. 2(a).

Each terminal A, B is divided into two segmental terminals 37, 38 eachhaving a semicircular ring shape, and includes a power supply bolt 40inserted into a bolt hole 39 extending through the heater base 33, a nut41 for fastening the power supply bolt 40 with the heater body 36 beinginterposed therebetween, and washers 42, 43. The segmental terminal 37is electrically connected only with the heater pattern 31, whereas thesegmental terminal 38 is electrically connected only with the heaterpattern 32. The segmental terminals 37, 38 are separated and insulatedfrom each other by a gap 44 extending in a radial direction, but oncethe power supply bolt 40 is fitted, a head 40a of the power supply bolt40 becomes in contact with both of the segmental terminals 37, 38 viathe washer 42 so that the heater patterns 31, 32 becomes electricallyconnected with each other to form the parallel-type heater 30. The powersupply bolt 40 and the washer 42 are made from insulating material suchas PBN. The washer 43 may be of insulating or non-insulating material.

FIG. 3 and FIG. 4 show the above-constructed parallel-type heater 30 ina state where the power supply bolt 40 is removed (or a halfway stateduring production of the heater 30 where the heater body 36 has beenobtained but the power supply bolt 40 is not yet fitted). As describedbefore, in this state, the segmental terminal 37 and the segmentalterminal 38 are insulated from each other by the gap 44, so that theheater pattern 31 is formed between the segmental terminals 37, 37 ofthe terminals A, B, and the heater pattern 32 is formed between thesegmental terminals 38, 38 of the terminals A, B, each forming a serialheater route 45, 46. Accordingly, in this state, the resistanceadjustment can be performed easily in the same way as for theaforementioned serial-type heaters 10 (FIG. 7).

The measurement points P21 to P24 are plotted along the heater patterns31, 32 in the same way as in the aforementioned conventionalparallel-type heater 20 (FIG. 8), and the resistance adjustment can beperformed in the following manner, which will now be described inreference to FIG. 5. In this example, the resistance value of the heater30 by design is 1.61 ohms (meaning that the resistance values of theroutes 45, 46 are both 3.22 ohms), wherein a section between theterminal A and the measurement point P1 should have a sectionalresistance value r21=1.26 ohms, a section between the measurement pointsP21 and P22 should have a sectional resistance value r22=1.19 ohms, asection between the measurement point P22 and the terminal B should havea sectional resistance value r23=0.77 ohms, a section between theterminal B and the measurement point P23 should have a sectionalresistance value r24=1.26 ohms, a section between the measurement pointsP23 and P24 should have a sectional resistance value r25=1.19 ohms, anda section between the measurement point P24 and the terminal A shouldhave a sectional resistance value r25=0.77 ohms (each sectionalresistance value r21 to r25 is a reference value after being adjusted).

In the state where the power supply bolt 40 is not yet fastened, theroute 45 is a serial route from the terminal A to the terminal B.Accordingly, in the same way as in the resistance adjustment for theserial-type heater 10 (FIG. 7) which has been described in reference toFIG. 9, it is possible to measure the resistance values between theterminal A and the measurement points P21, P22 and the terminal B andthen adjust them sequentially to become equal to the respectivereference values. Likewise, the resistance adjustment may be performedfor the route 46 as well. Thus, the resistance adjustment may be carriedout relatively easily. In practice, the element of the heater patterns31, 32 is formed at first a little bit thicker to provide a resistancevalue of a little bit smaller than the design resistance value, whichshould then be partly scraped depending upon the resistance valuesmeasured at the respective measurement points for the resistanceadjustment.

After the resistance adjustment has been performed for the imaginaryserial routes 45, 16 in the above-described manner, the power supplybolt 40, the nut 41 and the washers 42, 43 are fitted to each terminalA, B. Thus, as described before, a head 40a of the power supply bolt 40becomes in contact with both of the segmental terminals 67, 38 via thewasher 42 so that the heater patterns 31, 32 becomes electricallyconnected with each other to thereby form the parallel-type heater 30.

Embodiment 2

The above-described parallel-type heater 30 according to Embodiment 1has two heater patterns 31, 32 in parallel between a pair of terminalsA, B and therefore is designed such that each terminal A, B is dividedinto two segmental terminals 37, 38 separated by the radially-extendinggap 44. However, in case where more definite temperature control isrequired for a larger heater, for example, it may be designed such thata greater number of heater patterns, for example four heater patternsare formed in parallel between a pair of terminals A, B.

An example of such design is shown in FIG. 6. This parallel-type heater50 has four heater patterns 51-54 formed between terminals A, B, andeach terminal A, B is divided into four segmental terminals 55-58. Theheater pattern 51 (its center line being shown by a dashed line) isformed between the segmental terminals 55, 55 of the terminals A, B, theheater pattern 52 (its center line being shown by a broken line) isformed between the segmental terminals 56, 56 of the terminals A, B, theheater patterns 53 (its center line being shown by a dashed line) isformed between the segmental terminals 57, 57 of the terminals A, B, andthe heater patterns 54 (its center line being shown by a broken line) isformed between the segmental terminals 58, 58 of the terminals A, B.Each segmental terminal 55-58 is formed in a quarter-circular ringedshape, which is separated from each other by gaps 59 extending in radialand peripheral directions.

Although the present invention has been described in detail in referenceto the embodiments thereof, it is not limited thereto and may beimplemented in various modified applications. For example, although theheater patterns 31, 32 (the routes 45, 46) becomes electricallyconnected with each other via the washer 42 when the power supply bolt40 is fitted in Embodiment 1, it may also be designed that the bottom ofthe power supply bolt head 40a be in contact with the heater patterns31, 32 directly, which will require no washer 42. For a single heaterhaving plural terminal pairs, each terminal of each pair is divided intoa plural numbers of, for example, two (Embodiment 1) or four (Embodiment2) segmental terminals, the number thereof being corresponding to thenumber of the heater patterns formed in parallel between the terminals,so that imaginary serial patterns can be formed until the power supplybolts are fitted.

LEGENDS

-   10 serial-type heater (prior art)-   20 parallel-type heater (prior art)-   30 parallel-type heater (embodiment of the present invention)-   31, 32 parallel heater pattern-   33 heater base-   34 heater element-   35 overcoat-   36 heater main body-   37, 38 segmental terminal (divided into two)-   39 bolt hole-   40 power supply bolt-   41 nut-   42 washer-   43 washer-   44 gap-   45,46 route-   50 parallel-type heater (embodiment of the present invention)-   51-54 parallel heater pattern-   55-58 segmental terminal (divided into four)-   59 gap

1. A parallel-type heater wherein a plurality of heater patterns areformed in parallel between a pair of terminals to which power supplybolts are fitted respectively the parallel-type heater comprising: eachof said pair terminals is divided into a plurality of spaced segmentalterminals of the same number as said plurality of heater patterns, saidplurality of segmental terminals being electrically connected with eachother by said power supply bolt, a plurality of imaginary serial heaterpatterns arc formed between one of said segmental terminals divided fromone of said pair of terminals and one of said segmental terminalsdivided from the other pair of terminals when said power supply boltsare not yet fitted, said plurality of imaginary serial heater patternsbeing electrically connected with each other to form parallel circuitswhen said power supply bolts are fitted.
 2. The parallel-type heater ofclaim 1 wherein a head of said power supply bolt is in contact with aheater element forming said heater pattern directly or via a washer madeby conductive material.
 3. The parallel-type heater of claim 1 whereinfirst and second heater patterns are formed in parallel between a pairof said pair of terminals, each terminal being divided into a firstsegmental terminal to be electrically connected only with a first heaterpattern of said plurality of heater patterns and a second segmentalterminal to be electrically connected only with a second heater patternof said plurality of heater patterns.
 4. The parallel-type heater ofclaim 3 wherein each of said first and second segmental terminals isformed in substantially a semicircular ring shape, said first and secondheater patterns being insulated with each other by a gap extending in aradial direction between said segmental terminals.
 5. The parallel-typeheater of claim 1 wherein first to fourth heater patterns are formed inparallel between the pair of said terminals, each terminal being dividedinto a first segmental terminal to be electrically connected only withsaid first heater pattern, a second segmental terminal to beelectrically connected with said second heater pattern, a thirdsegmental terminal to be electrically connected with said third heaterpattern and a fourth segmental terminal to be electrically connectedonly with said fourth heater pattern.
 6. The parallel-type heater ofclaim 5 wherein each of said first to fourth segmental terminals isformed in substantially a quadrant ring shape, said first to fourthheater patterns being insulated with each other by gaps extending inradial and circumferential directions between said segmental terminals.7. A production of the parallel-type heater of claim 1, comprising:producing a heater body having a plurality of heater patterns inparallel between a pair of terminals, performing resistance adjustmentfor each of said imaginary serial heater patterns formed between onesegmental terminal of one terminal and one segmental terminal of theother terminal before fitting said power supply bolts to said terminals,and then fitting said power supply bolts to said terminals so that saidplural imaginary serial heater patterns become electrically connectedwith each other to form a parallel circuit.